Bin Contents: Single & Multiple Slit Stands, Diffraction Grating & Empty Stands, a small flash-light / torch, two red laser goggles, the screen, and the laser & adaptor.

NOTE: The goggles do not block the laser, they are designed to enhance the appearance of the laser so that you may avoid it.

Obtain an a black optical bench; lamps are also available; due to the fact that it’s impossible to block all light from the lab, it’s best to use the flash-light / torch that we provided the kit.

Use the front of the screen to locate its position on the bench; in the image above the screen was placed at the 100 cm mark.

The single slit stand doesn’t have a visual indicator; to determine which slit it is set to, either look through it or note the location as indicated by the plug in the image above.

The multiple slit stand doesn’t have a visual indicator; to determine which slit it is set to, either look through it or note the location as indicated by the plug in the image above.

Both single and multiple slit stands should be placed the following way in front of the laser.

Note: Never mix stands together; they are designed to be used separately.

The empty stand is intended for the hair; if hair is not available, you may use the thin black string.

Whether it’s hair or string, it must be taped vertically as shown in the image above.

The diffraction grating slide should be placed in the direction show (with the slide away from the laser).

Note: These slides are rated as 500 lines / mm!

The laser has two knobs that control its aiming; always adjust the aim so that the majority of the light passes through the object (slit, hair, grating, etc).

Typical single slit pattern; note the wide central maximum.

Tape either white or graph paper onto the screen and carefully draw the outlines of the maxima; this particular drawing was crude, it was made to show the method, be more careful! Use the rulers (NOT the triangles, templates, etc) to help you draw the lines if necessary.

With the ruler or the caliper, find the middle of the central maximum; this becomes the ‘zero’ for position measurements.

For the single slit (and the hair / string) we need the positions of the minima; the minima, statistically speaking, are usually in the geometric middles between the maxima; use the ruler or the caliper to find these middles and indicate them as shown.

Always remember to zero the caliper!

Measure the distance to the minima with respect to the center of the central maxima.

Measure the distance to the minima with respect to the center of the central maxima.

Due to the textures of hair or string being less than ideal, you get an overall fuzzier pattern; never the less if the hair or the string is thin enough, you will still be able to see a single slit like diffraction pattern.

Make exactly the same kind of drawing for the hair / string as you did for the single slit. 

Typical double slit pattern; note the wide central maximum contains within it internal maxima.

Note: The central maxima will always contain an odd number of these internal maxima.

In the figure above you will notice the wide central maximum contains 5 easily discernible internal maxima; but also notice that at its left and right ends there appear to be smaller and dimmer maxima; this gives you a total of 7 internal maxima; you need these seven for the measurements!

For the double slit case, we need the locations of the maxima; to do this, simply draw lines through the gaps between the maxima.

The lines in black were drawn over the gaps between the internal maxima; the actual positions of the maxima, however, are the geometric middles between the lines, these points were drawn as blue dots in the image above.

Indicate the location of the center of the center maximum; this will again be the ‘zero’ for determining positions.

Measure the location of the maxima (the blue dots) with respect to the center of the center maxima.

Measure the location of the maxima (the blue dots) with respect to the center of the center maxima.

The diffraction grating; to this experiment, the screen needs to be moved very close to the slide, until a total of 5 spots appear.

Another view of the 5 dots.

The pair of spots at the outer edges will be faint!

You can either encircle the spots or guestimate their middles.

Here we encircled the spots and used the ruler to approximate their middles; remember the exact locations of maxima (or minima) are always at the middles).

The center spot will again be the ‘zero’ for measurements.

The spots are maxima; label them accordingly. Note that negative orders imply negative values for position.

Measure the location of the maxima (indicated by the vertical lines in the image above) with respect to the center of the center maxima.

Measure the location of the maxima (indicated by the vertical lines in the image above) with respect to the center of the center maxima.